gemstone

Tumbled agate or chalcedony

Microcrystalline quartz (SiO₂), likely gray-brown agate/chalcedony

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent gray-brown body with subtle curved banding, waxy to vitreous luster, and no visible cleavage. The smoothly rounded shape indicates tumbling and polishing; exact identification is limited by the photograph.

Identified September 19, 2026More gemstone →

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Physical properties

Formation & geological history

Agate forms when silica-rich groundwater fills cavities in volcanic rock, depositing layered chalcedony over geologic time, commonly during the Cenozoic or older volcanic episodes. It is later cut and mechanically tumbled for decoration.

Uses & applications

Used for cabochons, beads, carvings, paperweights, and inexpensive jewelry; polished pieces are popular educational and collecting specimens.

Geological facts

Agate is a variety of chalcedony distinguished by cryptocrystalline quartz and commonly concentric or irregular color bands. Its color may be natural or enhanced by dye or surface coating.

Field identification & locations

Look for waxy luster, translucency at thin edges, curved internal banding, and resistance to scratching by steel; a glassy appearance or bubbles would suggest imitation glass. Common sources include Brazil, Uruguay, Mexico, India, and the United States.